Foundation mesh - How do you lap steel mesh sheets?

[CharLou]

Hi All,

I've a couple of questions regarding installing steel mesh in a slab and also in reinforced walls.

Q1:
Can anyone offer some advice on how to correctly lap steel mesh sheets?

Our raft requires us to add two layers of A393. The overall size of the slab is 11m x 8m. Whatever size sheets we use will mean up to four sheets will over lapping where they all meet.

I did something very similar several years ago and I remember having to cut out the corners of a couple of sheets. Was this correct?

Does anyone know what the correct way do this is?

Q2.
We also need to build a curved reinforced wall. No doubt we'll need to use bars not sheets.

Can anyone offer some tips on how to bend the bars to the desired shape?

Many thanks

[seanandruby]

I usually place the mesh one up and another upside down on top overlapped by two squares so the mesh is interlocked, may have to do two up and one down if you get my meaning. If you end up with high corners you might have to cut the the corners. If your radius is not to severe you should be able to pull the 'lacers' in.

[Tony McC]

Isn't it supposed to be a minimum 300mm overlap, and tied in place? Or has that vchganged too, now? It's a good while since I did any rebar work!

As Sean says, if the curve is, say, greater than about 3m radius, you can usually bend in-situ, but tighter than that it's often worth having the bars pre-bent by the supplier, especially if they are T20s or similar.

[CharLou]

Thanks gents. Appreciated

[GB_Groundworks]

General rule is 40x the diameter so a393 needs 400mm overlap

Get flying end mesh so you don't end up with a huge build up of steel in your overlap area ( has longer horizontals without the verticals so less build up of steel)

But maybe go read up a bit about concrete as it sounds you are pouring a big reinforced slab and are a little inexperienced very easy to get concrete wrong,

There are lots of pages on the main page about reinforced concrete

We often have to tie our own mesh now with bars bigger than 10mm doing a 20x11 slab x 400mm that's h16 at 100 centres gonna be good work out for the rebar guns

[CharLou]

Thanks. You're right, I don't do this often/never. At least nothing on such a large scale.

I'm only doing the prep, I'll be getting ground works firm sort the concrete, but I want to prepare the steel. I may have to bite-the-bullet and get someone in, but I think this is within my abilities.

As a follow up my engineer has emigrated since he prepared my drawings last year so I can't ask (an absolute pain), but he added a note on the drawings re Reinforced Retaining walls saying:

-----
7N Blockwork cavity wall with 150mm RC35 Concrete filled cavity with A393 mesh both faces.
-----

At the risk of sounding quite dumb, what does 'both faces' mean?

I assume this simply means two layers of A393 presumably spaced at 50mm.

This isn't something I'll be doing, but I need to know how much A393 I need to order when the time comes.


Thanks again.

[GB_Groundworks]

He means the front and back of the wall normal 50mm from the outside of the concrete so 60-70mm between them as the mesh is 20mm dependent on how you space it etc

[CharLou]

He means the front and back of the wall normal 50mm from the outside of the concrete so 60-70mm between them as the mesh is 20mm dependent on how you space it etc

Thanks, that's exactly what I needed to know.

Very much appreciated.